Conventionally, in an ion laser performing a laser oscillation by an energy transition owing to ionization of a gaseous active medium such as argon or krypton, it is necessary to increase ion density along with increasing an output level. In this case, a large electric current over 30 A may be charged. Therefore, for a discharge capillary and an envelope a material having a high thermal conductivity to effectively reject heat generated by a large electric current in the discharge section of the capillary and durable to high ion density plasma was needed.
Recently, silicon carbide(SiC) and aluminium nitride (AlN) as a material meeting such conditions are used. That is, in this case, SiC is used for a plasma capillary material and AlN is used for an envelope material. Also, AlN components are air-tightly sealed each other with frit glass for forming a laser tube.
A longitudinal section of a conventional ion laser tube is shown in FIG. 3. The bore material 1 made up of SiC having a capillary tube hole 2 in the center and the flange 3 is inserted to the envelope 4 made up of AlN and sealed by the high fusing point glass 6, thus the capillary composite component 7 is formed. Next, a plurality of capillary composite components 7 are coaxially and air-tightly sealed each other by an appropriate jig (not shown in the figure) and the high fusing point glass 8 made up of a zinc/boric acids material. Then, the hollow pipe 11 made up of AlN is sealed for including the anode 9 and cathode 10. The tubular components made up of boro-silicate glass 13 (hereinafter referred to as a KB glass component) are air-tightly sealed at the both sides of the hollow pipes with the low fusing point glass 12 made up of a lead/sillic acids material, thus the discharge capillary path 14 is formed. FIG. 4 is an enlarged cross section of the sealing section of the conventional hollow pipe 11 made up of AlN and the KB glass component 13. The hollow pipe 11 made up of AlN and the KB glass component 13 are sealed only with the low fusing point glass 12 made up of a lead/sillic acids material. Like this, in the conventional ion laser tube the fusing point glass 12 made up of a lead/sillic acids material of which sealing temperature is low is used for sealing, because the distortion point of the KB glass component 13 having the similar coefficient of thermal expansion to AlN is low such as 500.degree. C. and it is impossible to seal with the high fusing point glass 8 made up of a zinc/boric acids material.
More, the end plates 15 respectively having the anode 9 and the cathode 10 are connected to the respective end portions of the discharge capillary path 14, the respective glass valves 16 are connected to end portions of the end plates 15, further the Brewster windows 17 are connected to the end portions of glass valves 16. After that, argon gas of the pre-determined quantity is sealed. Thus, the ion laser tube is completed.
However, in the above-mentioned conventional ion laser tube, there is a problem that the low fusing point glass made up of a lead/sillic acids material used in the ion laser tube is low in heat resistance and the lead(lead oxide) component included in the low fusing point glass made up of a lead/sillic acids material reacts with aluminium (Al) in the AlN surface and nitrogen (N.sub.2) is generated on the sealing interface at the time of sealing of the hollow pipe 11 made up of AlN and the KB glass component 13. As the result, a defect such as many bubbles are generated on the sealing interface occurs and air-tightness at the sealing section is failed. Conventionally, a bubble occupation area ratio to the sealing area is over 50%.